Digital control device

Abstract

A digital control device includes a first controller which generates a control reference signal of a first controlled variable of a controlled system, a first frequency converter which converts said control reference signal into pulses of a frequency proportional to a magnitude thereof, a second frequency converter which converts a measured value of a second controlled variable of said controlled system into pulses of a frequency proportional to a magnitude thereof, and a second controller which obtains a difference between the output pulses of said first frequency converter and the output pulses of said second frequency converter and which controls said second controlled variable by using said difference as a control reference value.

What is claimed is: 
     
       1. A digital control device comprising a first controller which generates a control reference signal of a first controlled variable of a controlled system, a first frequency converter which converts said control reference signal into pulses of a frequency proportional to a magnitude thereof, a second frequency converter which converts a measured value of a second controlled variable of said controlled system into pulses of a frequency proportional to a magnitude thereof, and a second controller which obtains a difference between the output pulses of said first frequency converter and the output pulses of said second frequency converter and which controls said second controlled variable by employing said difference as a control reference value; wherein said second controller comprises a pulse canceller circuit which subtracts said output pulses of said frequency converter from said output pulses of said first frequency converter and which feeds back the resulting difference and subtracts it from said output pulses of said first frequency converter.   
     
     
       2. A digital control device according to claim 1, wherein said controlled system is a thyristor circuit which drives a motor. 
     
     
       3. A digital control device according to claim 2, wherein said first controlled variable is a current, while said second controlled variable is a voltage.